Electric heating tube in which enlarged convolutions of filament coil act as filament supports



Dec. 14, 1965 R. EGGERS 3,223,375 ELECTRIC HEATING TUBE IN WHICH ENLARGED CONVOLUTIONS OF FILAMENT COIL ACT AS FILAMENT SUPPORTS Filed Dec. 15, 1959 United States Patent ELECTRIC HEATING TUBE IN WHICH EN- LARGED CONVOLUTIONS 0F FILAMENT COIL ACT AS FILAMENT SUPPORTS Reinhold Eggers, Burgau uber Riedlingen, Wurtternberg, Germany Filed Dec. 15, 1959, Ser. No. 859,820 4 Claims. (Cl. 313-273) The present invention relates primarily to electric high intensity heating tubes.

Electric heating tubes are employed for many different purposes, for example, for drying and baking paints and enamels, for softening plastics, for baking, roasting, or grilling food, etc.

There is a prevailing tendency to attain the highest possible output of radiant heat with tubes of the smallest possible dimensions. Thus, for example, there are known heaters in which a helically wound coil of tungsten wire is mounted in a quartz tube with the axis of the helix extending in the longitudinal direction of the tube. It is, however, very difficult to maintain such a tungsten coil in a coaxial position within the tube. It has for this purpose been proposed prior to this invention to insert small plates of molybdenum into the coils to serve as supports. However, in order to attain a coil which will operate properly for a long time, it is necessary to preheat the coil at a very high temperature prior to the installation which renders the coil brittle. Since the subsequent insertion of the small molybdenum plates causes a slight deformation of the coil, this deformation often leads to breakage of the coil. The use of such small molybdenum plates for supporting the tungsten coil also has the disadvantage that a considerable drop in temperature occurs at the points of contact between the molybdenum plates and the incandescent coil, so that the coil will not produce heat uniformly over its length.

It is an object of the present invention to provide electric heating tubes of the highest possible heat output which overcome the above-mentioned disadvantages.

According to the present invention, the heating coil is designed so that a few of the windings of the coil, which are disposed at suitable distances from each other, rest upon the wall of the tubular enclosure and form supporting elements.

The heating tube according to the invention therefore contains a self-supporting heating coil which extends exactly coaxially with the quartz tube or other suitable tubular enclosure. The coil supports, are current-carrying integral components of the coil itself, and therefore radiate heat as the other portions of the coil. Thus the heat dissipation from the coil caused by the metal supporting plates of the known heating tubes is avoided. Since the supporting parts according to the invention are integral components of the coil, no deformations of the coil after initial shaping will occur. The coils according to the invention have the further advantage of being more easily inserted into the tubular enclosure since they cannot cause any binding or wedging. They are also superior to the known coils in having a much longer life.

The supporting parts which according to the invention are formed by the windings of the coil itself are pref- I 3,223,875 Patented Dec. 14, 1965 The encasing tube may be partly provided with a lightreflecting coating. Thus, for example, a longitudinally extending reflecting strip may be deposited by metallization on the outside of the tube so that all rays emitted by the heating coil will be directed toward the other side of the heating tube where they are to be utilized.

In some applications of high-intensity heaters, light radiation is undesirable, for example, in kitchen apparatus. of the radiation, the encasing tube of the heater which consists of quartz or a special glass may be suitably colored, for example, ruby-red, black, or the like.

These and other objects, features, and advantages of the present invention will become further apparent from the following detailed description thereof, particularly when the same is read with reference to the accompanying drawings, in which,

FIGURE 1 shows a side view of an electric heating tube according to the invention;

FIGURE 2 shows a cross section thereof; while FIGURE 3 shows a similar cross section of a heating tube according to a modification of the invention.

Referring to the drawings, and initially to FIGS. 1 and 2, the electric heater according to the invention consists of a heating coil 2 of tungsten wire which is enclosed within a vacuum-tight tube 3 of quartz or a similar heat-resistant material and extends therein in the axial direction. The ends of the heating coil 2 are connected to fused-in vacuum-tight leads 4 and the quartz tube 3 is evacuated. Heating coil 2 is wound so that at regular distances individual coil windings of the tungsten wire which is otherwise helically wound are bent outwardly so as to define, for example, a triangle, as shown in FIGURE 2, the outer circumference of which corresponds to or is slightly smaller than the inner di arneter of the quartz tube so that the triangle is inscribed in a circle substantially identical with the circle formed by the cross section of the cavity in the tube 3. These substantially triangular windings of coil 2 form supporting parts 1 which maintain the coil in a central position within the quartz tube 3.

FIGURE 3 illustrates a modification of the coil 2, in which the regularly spaced windings 1 are bent into a fiat elliptical shape 1 inscribed into the circular cross section of the tube cavity.

The encasing tube 3' shown in FIG. 3 is partly provided with a light reflecting coating 5. The coating is a longitudinally extending reflecting metal strip deposited on the outside of the tube 3' by metallizing. The rays emitted by the heating coil 2 are directed by the coating 5 toward the other side of the tube. The encasing tube 3' is colored ruby red to filter out most visible light radiation while passing radiant heat.

The two illustrated particular shapes of the supporting windings 1, 1 of the heating coil 2 are mere examples of some of the many suitable shapes in which the heating coil may be wound.

In order to produce the heating coils according to the invention, a tungsten wire or a wire of another suitable refractory material is wound upon a round wire core and the winding operation is interrupted at certain intervals. A winding which serves as a supporting part 1 is then wound over a die, for example, of triangular shape, whereupon winding is continued for the required distance on the round core until the next specially shaped winding is to be formed.

The completed coil is heated on the winding core to such a high temperature that no deformation will occur in service.

The present invention facilitates the production of heating tubes and other vacuum tubes in which filaments of a similar type may be used. The number of rejects In order to filter out the undesirable wave lengths which occur during the production of these tubes is extremely small. The high-intensity. heating tube accord-, ing to the invention is therefore relatively inexpensive and it has the further advantage of radiating heat at a uniform temperature along its entire length. As already indicated, the invention is not limited to heating tubes but may also be applied to other incandescent or vacuum tubes which are intended for other purposes and in which the wire filament should be maintained in awell defined position. A

Although my invention has been illustrated and described with reference to the preferred embodiments thereof, I wish to have it understood that it is in no way limited to the details of such embodiments, but is capable of numerous modifications within the scope of the appended claims. 7

Having thus fully disclosed my invention, what I claim is:

1. Electric heat-generating. device comprising a hermetically sealed tubular enclosure having two ends, an inside wall, and an inside diameter, two conductors sealed through said ends,.and an integral coiled filament extending approximately centrally within said enclosure and being connected at its ends to said conductors, said coiled filament including a-main portion of smaller convolutions and at least a single larger convolution, said main portion having a substantially cylindrical shape and an outside diameter smaller than said inside diameter, said single larger convolution being shaped to provide point-contacts with said inside wall and thus to, position said. filament.

2. In the device according to claim 1, said convolution, when viewed in plan, having the outline of a paper 1 clip, and being adapted to engage said inside Wall in two points.

3. In the device according to References Cited by the Examiner UNITED STATES PATENTS 2,342,044 2/1944 Foote 313279 X 2,523,033 9/1950 Leighton 313-279 2,859,368 11/1958 Biggs et al 219-34 X 2,864,025 12/1958 Foote et a1. 313279 2,883,571 4/1959 Fridrick et al. 313-222 2,957,154 10/1960 Strokes 21934 HERMAN KARL SAALBACH, Primary Examiner.

ARTHUR GAUSS, JOHN W. HUCKERT, GEORGE N. WESTBY, Examiners.

claim 1, ,said convolution, when viewed in plan, being substantially V-shaped, 

1. ELECTRIC HEAT-GENERATING DEVICE COMPRISING A HERMETICALLY SEALED TUBULAR ENCLOSURE HAVING TWO ENDS, AN INSIDE WALL, AND AN INSIDE DIAMETER, TWO CONDUCTORS SEALED THROUGH SAID ENDS, AND AN INTEGRAL COILED FILAMENT EXTENDING APPROXIMATELY CENTRALLY WITHIN SAID ENCLOSURE AND BEING CONNECTED AT ITS ENDS TO SAID CONDUCTORS, SAID COILED FILAMENT INCLUDING A MAIN PORTION OF SMALLER CONVOLUTIONS AND AT LEAST A SINGLE LARGER CONVOLUTION, SAID MAIN PORTION HAVING A SUBSTANTIALLY CYLINDRICAL SHAPE AND AN OUTSIDE DIAMETER SMALLER THAN SAID INSIDE DIAMETER, SAID SINGLE LARGER CONVOLUTION BEING SHAPED TO PROVIDE POINT-CONTACTS WITH SAID INSIDE WALL AND THUS TO POSITION SAID FILAMENT. 